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Anesthesia Pharmacology > Exam 4 - Local Anesthetics > Flashcards

Exam 4 - Local Anesthetics Flashcards

1
Q

What was the first local anesthetic?
What class is it?

A

Cocaine
Ester

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2
Q

What was cocaine first used for and what was the effect?

A

Ophthalmology

Local vasoconstriction: shrink nasal mucosa.

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3
Q

What was the first synthetic ester developed in 1905?

A

Procaine

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4
Q

What was the first synthetic amide developed in 1943?

A

Lidocaine

Gold Standard

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5
Q

What are the uses Local Anesthetics (LAs)?

A
  • Treat dysrhythmias
  • Analgesia: Acute and chronic pain
  • Anesthesia- ANS Blockade, Sensory Anesthesia, Skeletal Muscle Paralysis
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6
Q

What antiarrhythmic Drug Class is lidocaine in?

A

Class I: Sodium Channel Blockers

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7
Q

MAGA: What is the intra-op infusion dose of lidocaine?

A

1 mg/kg over an hour

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8
Q

What is the IV bolus and drip dose of Lidocaine?

When should lidocaine be terminated?

A
  • 1 to 2 mg/kg IV (initial bolus) over 2 - 4 min.
  • 1 to 2 mg/kg/hour (drip)
  • terminated 12 - 72 hours
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9
Q

What are considerations of lidocaine?

A

Careful monitoring: cardiac, hepatic, renal dysfunction

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10
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 1-5 mcg/ml.

A

Analgesia

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11
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 5-10 mcg/ml.

A
  • Circum-oral numbness
  • Tinnitus
  • Skeletal muscle twitching
  • Systemic hypotension
  • Myocardial depression
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12
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 10-15 mcg/ml.

A
  • Seizures
  • Unconsciousness
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13
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is 15-25 mcg/ml.

A
  • Apnea
  • Coma
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14
Q

Dose Dependent Effects of Lidocaine if plasma lidocaine concentration is >25 mcg/ml.

A
  • Cardiovascular Depression
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15
Q

How can lidocaine SQ help start IVs?

A

Causes local vasodilation

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16
Q

Describe the components that make up the molecular structure of lidocaine.
What about the structure makes a LA an amide or ester?

A

Lipophilic Portion (Aromatic Section)
Hydrocarbon Chain
Hydrophilic (Amino Group)

Bond between the lipophilic portion and the hydrocarbon chain will determine if LA is an ester or an amide.

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17
Q

Ester or amide determination is based upon which portion of the molecular structure?

A

Intermediate chain

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18
Q

What 2 other drugs are mixed with LA and why?

A

Epinephrine - increases duration of the drug (reduces spread from desired site)
Sodium Bisulfite - increases solubility to epinephrine

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19
Q

Composition of LA will have a pH of ____ and are weak _______ ?

A

pH of 6; weak bases

A majority of LA are weak bases

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20
Q

What are the ester and amide local anesthetics?

A

Amides (have 2 i’s)

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21
Q

What LA have a potency of 1?

A

Procaine, lidocaine, prilocaine, and mepivacaine

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22
Q

Which LA will have a potency of 16?

A

Tetracaine

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23
Q

Which LAs will have a potency of 4?

A

Chloroprocaine
Bupivacaine
Levobupivacaine
Ropivacaine

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24
Q

Which LAs will have rapid onset?

A

Chloroprocaine
Lidocaine

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25
Q

Which 3 LA will have the highest protein binding?

A

Levobupivacaine (>97%)
Bupivacaine (95%)
Ropivacaine (94%)

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26
Q

Lipid solubility correlates to _______ of the drug.

Which LA has the highest lipid solubility?

A

potency

Tetracaine

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27
Q

What is the general rule between fraction non-ionized and potency?

A

The higher % non-ionized, the more potent

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28
Q

What are Liposomes used for?

A
  • Used to upload a higher amount of LA into a molecule & have a consistent release of LA in the tissues.
  • Prolonged duration of action & decreased toxicity
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29
Q

FDA released what LA drug that contains liposomes and can last up to 96 hours.

A

Bupivacaine ER (Exparel)

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30
Q

MOA of Local Anesthetics

A
  • Binds to voltage-gated Na+ channels (must be inactivated and closed)
  • Block/inhibit Na+ passage in nerve membranes

LA must be non-ionized and lipid-soluble to go through the cell membrane and block the Na+ gated channel from within the cell.

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31
Q

3 factors affecting LA blockade?

A
  • Lipid solubility or non-ionized form
  • Repetitively stimulated nerve (↑ sensitivity)
  • Diameter of the nerve (↑ diameter, ↑ LA dose)
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32
Q

What happens when you expose LA (a weak base) to an acidic environment?

A

LA becomes ionized.
When LA becomes ionized, it will not cross cell membrane to block Na+ gated channels.

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33
Q

Besides Na+ channels, what are the other sites of action for LA?

A
  • Potassium channels
  • Calcium Ion Channels
  • G protein-coupled receptors
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34
Q

Minimum Effective Concentration or Cm (LAs) = _________ (Volatile Agents)

A

MAC

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35
Q

What component of the local anesthetic is required for the conduction block?

A

Non-ionized form (equates with lipid solubility) - needs to be able to cross the cell membrane and block Na+ from the inside

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36
Q

Larger fibers need _____ concentrations of LAs.

37
Q

The diameter of the motor nerve is how many times larger than the diameter of the sensory nerve.

A

Twice as large in diameter

38
Q

How many nodes of Ranvier need to be blocked to equate to 1 cm of local anesthesia blockade?

A

At least 2, preferably 3 Nodes of Ranvier to prevent the conduction (Minimum Effect Concentration)

39
Q

Which nerve fibers are blocked most rapidly?

A

Pre-ganglionic B fibers (SNS)

40
Q

These pain fibers require equivalent doses of LA?

A
  • Myelinated A-δ and unmyelinated C-fibers
41
Q

Which patient population will have increased sensitivity and require a smaller dose?

42
Q

Pharmacokinetics of LA

If pKa is close to physiological pH, how does this affect the onset of action?

A

Rapid onset of action

43
Q

When administering LA, only ______% of the drug is in lipid-soluble nonionized form.

44
Q

If a LA has intrinsic vasodilator activity, what happens to its potency?

What happens to the duration of action?

A

LA is less potent

↓ Duration of action

Spreads from intended site

45
Q

Because Lidocaine has vasodilator activity, there is ____ systemic absorption. Resulting in a ____ duration of action.

A

greater
shorter

46
Q

4 factors that influence the absorption of LA.

A
  • Site of injection
  • Dosage
  • Epinphrine use (increased DOA)
  • Pharmacologic characteristics of the drug
47
Q

List the uptake of Local Anesthetics Based on Regional Anesthesia Technique from highest blood concentration to lowest blood conc.

A

“I Tried Coffee Plus Espresso, But Shaky Start!”

48
Q

____ is the primary determinant of potency

A

Lipid solubility

49
Q

The rate of clearance is dependent on what two factors?

A
  • Cardiac output
  • Protein binding: % bound is inversely related to % plasma. (40% albumin-bound means 60% will float freely in plasma.)
50
Q

Which LA will metabolize the fastest?

A

Chloroprocaine d/t the 0% of protein binding.

51
Q

Which LA will metabolize the slowest?

A

Levobupivacaine d/t the highest % of protein binding.

52
Q

Why is it important to know the metabolizing rate of LA.

A

Re-dosing of LA

53
Q

Metabolism of Amides.
Location of Metabolism:
Most rapidly metabolized drug:
Intermediate:
Slow:

A

Location of Metabolism: Microsomal enzyme (Liver)
Most rapidly metabolized drug: Prilocaine
Intermediate: Lidocaine, Mepivacaine
Slow: Levobupivicaine, Bupivacaine, Ropivacaine

Metabolism is dependent on protein binding! Less protein bound → higher plasma conentration → more metabolized

54
Q

Metabolism of Esters?
Exception?

A

Hydrolyzed by cholinesterases in plasma, except cocaine which is metabolized by the liver.

55
Q

What is the metabolite of esters?

What is the significance of this metabolite?

A

ParaAminoBenzoic acid (PABA)
Allergic reactions

56
Q

Is there cross-sensitivity between an amide allergy to an ester allergy?

57
Q

Which class of LA has a slower metabolism

A

Amides are slower at metabolism.

58
Q

What are the most common LAs that have first-pass pulmonary extraction?

A
  • Lidocaine
  • Bupivacaine (dose dependent)
  • Prilocaine
59
Q

The poor water solubility of local anesthetics usually limits renal excretion of unchanged drug to less than ____ %

The exception is ____ , of which 10% to 12% of unchanged drug can be recovered in urine.

Water-soluble metabolites of local anesthetics, such as ____ resulting from metabolism of ester local anesthetics, are readily excreted in urine.

A

The poor water solubility of local anesthetics usually limits renal excretion of unchanged drug to less than 5%

The exception is cocaine, of which 10% to 12% of unchanged drug can be recovered in urine.

Water-soluble metabolites of local anesthetics, such as PABA resulting from metabolism of ester local anesthetics, are readily excreted in urine.

60
Q

In general, the more lipid soluble the local anesthetic is, the greater the potency. T/F

61
Q

Which local anesthetic property is most important regarding the duration of action?

A

Protein Binding (most important)

More protein bound → prolonged release from proteins → plasma conc stay elevated longer

62
Q

How does pregnancy affect admistration of local anesthetics?

A
  • Lower levels of plasma cholinesterases = require decreased doses of ester LA
  • Amides have significant transfer to the placenta and lead to ion trapping
63
Q

What determines the rate and degree of diffusion of local anesthetics across the placenta?

A
  • Plasma protein binding
  • Determines amount of free or unbound drug available in the blood
64
Q

What classification of LAs is more likely to cause ion trapping?

A

Amides
Esters are hydrolyzed rapidly so they do not readily cross the placenta

Ion trapping will lead to LA toxicity in the placenta.

65
Q

Describe ion trapping during pregnancy?

A

The pH in the fetal environment is more acidic than in maternal circulation (fetal pH 7.3-7.35). LA becomes ionized and trapped in the fetal circulation.

66
Q

If there is ion trapping in the placenta, what can be given to adjust the pH?

A

Sodium Bicarb

67
Q

Bupivacaine
Protein Bound:
Arterial Concentration:

A

Bupivacaine
Protein Bound: 95%
Arterial Concentration: 0.32

68
Q

Lidocaine
Protein Bound :
Arterial Concentration:

A

Lidocaine
Protein Bound: 70%
Arterial Concentration: 0.73

69
Q

Prilocaine
% Protein Bound
Arterial Concentration

A

Prilocaine
Protein Bound: 55%
Arterial Concentration: 0.85

70
Q

Lidocaine
Metabolite:
What will affect metabolism and elimination:

A

Lidocaine
Metabolite: Xylidide
What will affect metabolism and elimination: Hepatic disease

71
Q

What is Lidocaine max infiltration dose (plain and w/ epi)?

A

Maximum infiltration dose:
300 mg plain
500 mg with EPI (Rate of distribution is slower with epinephrine, so we can give more lidocaine.)

72
Q

How will Pregnancy Induced Hypertension affect lidocaine clearance?

A

Prolong clearance
Systemic vacoconstricion reduces hepatic blood flow

73
Q

Prilocaine metabolite.

What is the issue with this metabolite?

A

Metabolite: Ortho-toluidine

The metabolite oxidizes Hemoglobin to Methemoglobin, resulting in Methemoglobinemia (doses > 600 mg can cause symptoms)

74
Q

What is the result of Methemoglobinemia?

A

Cyanosis due to decreased O2 carrying capacity

75
Q

Treatment of Prilocaine induced methemoglobinemia?

A

Methylene Blue
1 to 2 mg/kg IV over 5 mins (initial dose) - dont exceed 7-8mg/kg

76
Q

Mepivacaine is similar to Lidocaine except:

A
  • Longer duration of action
  • Lacks vasodilator activity
  • Prolonged elimination in fetus & newborn
  • No Mepivacaine in OB patients
77
Q

What is bupivacaine bound to?

A

95% bound to α1-Acid glycoprotein

78
Q

Ropivacaine
Metabolized by ____
Metabolites can accumulate with ____ patients
____ system toxicity than Bupivacaine
94% protein bound to ____

A

Ropivacaine
Metabolism: P450 enzymes
Metabolites: Can accumulate with uremic patients
Lesser system toxicity than Bupivacaine
94% protein bound to α1-acid glycoprotein

79
Q

Dibucaine
Metabolism:
Enzyme Inhibition:

A

Dibucaine
Metabolism: Liver
Enzyme Inhibition: inhibits the activity of normal butyrylcholinesterase (plasma cholinesterase) by more than 70%

This LA is used to test for atypical plasma cholinesterase.

80
Q

Procaine Metabolite:

A

Procaine Metabolite: PABA (ester anesthetics), excreted unchanged in the urine

81
Q

Chloroprocaine metabolizes ____ times faster than Procaine.

Pregnancy decreases plasma cholinesterase by ____%

A
  • 3.5x faster than procaine
  • 40%
82
Q

Which ester LA has the slowest metabolism?

A

Tetracaine d/t 76% protein bound

83
Q

Which LA will have the highest rate of metabolism by hydrolysis?
Procaine
Chloroprocaine
Tetracaine

A
  • Chloroprocaine (fastest metabolism, 0% protein bound)
  • Procaine (6% protein bound)
  • Tetracaine (slowest, 76% protein bound)
84
Q

Benzocaine use:

A

Uses: Topical anesthesia of mucous membranes:
Tracheal intubation, Endoscopy, Transesophageal echocardiography (TEE), Bronchoscopy

Benzocaine comes in a spray.

85
Q

Benzocaine
Onset:
Duration:
Dose: Brief spray (20%) =
Overdose of Benzocaine can lead to ________.

A

Benzocaine
Onset: Rapid
Duration: 30 to 60 minutes
Dose: Brief spray (20% concentration) = 200 to 300 mgs
OD of Benzocaine can lead to Methemoglobinemia

86
Q

What makes Benzocaine unique?

A

Weak acid instead of a weak base, like most LA.
pKa = 3.5

87
Q

How is cocaine metabolized?

Who should receive decreased amounts of cocaine?

A

Metabolized by plasma and liver cholinesterase

Decrease cocaine use in parturients, neonates, the elderly, and severe hepatic disease

88
Q

Cocaine
Peak:
Duration:
Elimination:

A

Cocaine
Peak: 30 to 45 mins
Duration: 60 minutes after peak
Elimination: Urine (24 to 36 hours)

89
Q

Adverse side effects of cocaine.

A

Cocaine is a stimulant; use it with caution.

Cocaine can cause coronary vasospasm, ventricular dysrhythmias, HTN, tachycardia, and CAD.

Anesthesia Pharmacology (19 decks)

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